Immune reactions in the body take place locally, and are commonly characterized by the infiltration of immune cells. Specifically, efficient immune reactions are not achieved without adequate mobilization of the required immune cells to local sites. Further, the types of infiltrating immune cell vary depending on the tissues and diseases. For example, a large number of Th1 cells producing interleukin (IL)-12, interferon (IFN)-γ, or such accumulate in joints with rheumatoid arthritis, while many Th2 cells producing IL-4, IL-5, or such accumulate in asthmatic lungs. By elucidating the cell infiltration mechanism allowing such selective cell infiltration, it is thought that infiltration of specific cells can be suppressed and the diseases of immune reactions can thereby be controlled.
The infiltration of immune cells is roughly divided into four steps: (1) loose contact with vascular endothelial cells via secretin; (2) integrin activation by chemokine receptors; (3) strong adhesion to vascular endothelial cells via integrins; and (4) extravascular migration through intercellular spaces between vascular endothelial cells. The molecular mechanisms underlying the first three steps have been elucidated; however, the extravascular migration is still poorly understood.
JAM-A and PECAM-1 have recently been reported as molecules involved in extravascular migration. JAM-A and PECAM-1 are cell membrane proteins belonging to the immunoglobulin superfamily (IgSF), and function as cell adhesion molecules.
The JAM family, comprising JAM-A, JAM-B, and JAM-C, comprise two extracellular Ig-like domains and are reported as being expressed in epithelial cells, endothelial cells, leukocytes, platelets, and the like. In addition to homophilic binding, binding to integrin αLβ2 has been reported for JAM-A. Binding to integrin α4β1 and JAM-C, in addition to homophilic binding, have been reported for JAM-B. JAM-C has been reported as binding to JAM-B and integrin αMβ2, but not as binding in a homophilic manner. Thus, through such homophilic or heterophilic binding, JAM family molecules are involved in adhesion between endothelial cells, between leukocytes and endothelial cells, and between platelets and endothelial cells.
In addition to the JAM family, many other molecules comprising two extracellular Ig-like domains exist. There are reports that some of these show similar localizations to molecules of the JAM family. For example, the coxsackie and adenovirus receptor (CAR) was identified as a receptor for coxsackie viruses and adenoviruses and is localized in tight junctions and adherence junctions in epithelial cells and endothelial cells (Non-Patent Documents 1 and 2). Further, the endothelial-selective adhesion molecule (ESAM) was identified as a molecule selectively expressed only in endothelial cells, but was then reported as being expressed in platelets as well.
To control diseases involving immune cells, it is extremely important to investigate whether such molecules belonging to IgSF are associated with the adhesion of epithelial cells, endothelial cells, leukocytes, and platelets, and to elucidate the mechanism underlying cell infiltration.    [Non-Patent Document 1] Cohen C. J., Shieh J. T., Pickles R. J., Okegawa T., Hsieh J. T., Bergelson J. M., Proc. Natl. Acad. Sci. USA, (2001) 98(26):15191-15196.    [Non-Patent Document 2] Walters R. W., Freimuth P., Moninger T. O., Ganske I., Zabner J., Welsh M. J., Cell, (2002) 110(6):789-799.    [Non-Patent Document 3] Moog-Lutz C., Cave-Riant F., Guibal F. C., Breau M. A., Di Gioia Y., Couraud P. O., Cayre Y. E., Bourdoulous S., Lutz P. G., Blood, (2003) 102(9):3371-3378.